Method for indicating quality of a circuit board

ABSTRACT

A circuit board with a quality-indicator mark and a method for indicating quality of the circuit board. The circuit board includes a plurality of circuit board units. A plating bus is formed around each circuit board unit and extended to form a plating trace in an inner-layer circuit structure of each circuit board unit. The inner-layer circuit structure is inspected in quality to maintain or break connection between the plating trace and plating bus if the quality is good or not. At least one circuit structure is formed on the inner-layer circuit structure and electrically connected to the plating trace to form a conductive mark on each circuit board unit. A metal protection layer is formed on the at least one circuit structure via the plating bus, and the conductive mark with the metal protection layer indicates that the inner-layer circuit structure of the circuit board unit is good.

FIELD OF THE INVENTION

The present invention relates to circuit boards with quality-indicatormarks and methods for indicating the quality of the circuit boards, andmore particularly, to a multi-layer circuit board formed on a surfacethereof with a mark for indicating whether inner-layer circuits of thecircuit board are good, and an indication method thereof.

BACKGROUND OF THE INVENTION

With development in the electronic industry, electronic products havebeen developed toward providing multiple functions and highperformances. In order to achieve high integration and sizeminiaturization of a semiconductor package, a circuit board for carryingmultiple active/passive components and circuits has evolved from adouble-layer board to a multi-layer board, wherein an available circuitarea of the multi-layer circuit board is enlarged via interlayerconnection technology within a limited space for accommodatingintegrated circuits with a high circuit density.

Moreover, due to an increase in popularity of portable products such ascommunication, network and computer products etc., BGA (ball grid array)packages, flip-chip packages, CSPs (chip size packages) and MCM (multichip module) packages have become mainstream products in the market asthey are incorporated with size-reduced integrated circuits (ICs) andhave a high density and a large number of leads or input/output (I/O)connections. These packages are usually cooperative with high capabilitychips such as microprocessors, chip modules and graphics chips etc. toachieve higher speed operation. However, fabrication limitations of anIC package substrate with circuits on the functions thereof such as chipsignal transmission, bandwidth improvement and control resistance,impede the use of such substrate in a package with a large number of I/Oconnections. As the package size is reduced to approximately the chipsize, how to develop a package substrate with fine circuits and a highdensity of fine vias is an important research task.

Accordingly, a conventional method for fabricating a multi-layer circuitboard by using build-up technology has been provided. FIGS. 1A to 1Dshow a build-up method for fabricating a multi-layer circuit board, andthis build-up method generally includes two steps: preparing a core andperforming a circuit build-up process. Referring to FIG. 1A, first, acore 11 is prepared, which comprises a resin core layer 111 with apre-determined thickness and circuits 112 formed on front and backsurfaces of the resin core layer 111. A plurality of plated throughholes 113 are formed in the resin core layer 111 to electrically connectthe circuits 112 on the front and back surfaces of the resin core layer111. Then referring to FIG. 1B, a build-up process is performed on thecore 11 to form a dielectric resin layer 12 on the front and backsurfaces thereof respectively, and the dielectric resin layer 12 isprovided with a plurality of blind vias 13 for exposing portions of thecircuits 112. Referring to FIG. 1C, a metal conductive film 14 isdeposited on an exposed surface of the dielectric resin layer 12, sidewalls of the blind vias 13 and the exposed portions of the circuits 112by means of an electroless plating or sputtering technique, and apatterned dry film 15 is formed on the metal conductive film 14. Thepatterned dry film 15 has a plurality of openings 150 for exposingportions of the conductive film 14 on which a patterned circuit layer isto be formed. Finally referring to FIG. 1D, a patterned circuit layer 16is formed in the openings 150 of the dry film 15 by an electroplatingtechnique, wherein the patterned circuit layer 16 is electricallyconnected to the circuits 112 through the blind vias 13, and then thedry film 15 and the part of the conductive film 14 covered by the dryfilm 15 are removed by etching, such that a build-up structure 10 a isfabricated on each of the front and back surfaces of the core 11 so asto achieve a 1+2+1 substrate 10 with multi-layer circuitry (i.e. 2build-up structures and a double-layer core). Similarly, the abovebuild-up process may be repeated to form a second build-up structure onthe build-up layer 10 a (referred to as “first build-up structure”) soas to fabricate a 2+2+2 substrate with multi-layer circuitry. Relatedprior arts include U.S. Pat. Nos. 5,837,427, 5,994,771 and 6,384,344.

Subsequently, BGA semiconductor packaging processes are readilyperformed, which allow a semiconductor chip to be mounted on a frontsurface of the foregoing substrate with desirable circuitry, and allow aplurality of solder balls to be implanted on a back surface of thesubstrate, wherein the solder balls are used to electrically connect theBGA package to an external electronic device such as printed circuitboard (PCB). In order to reduce the weight and size of electronicproducts, there is provided a TFBGA (thin and fine ball grid array)package having a smaller overall size than the conventional BGA package.The TFBGA packages are normally fabricated in a batch manner on asubstrate strip, wherein the substrate strip is predefined with aplurality of package sites each for forming a single TFBGA package. Asingulation process is finally performed to separate apart the pluralityof package sites to form a plurality of individual TFBGA packages.

Generally to provide electrical connection and bonding of asemiconductor package to an external electronic device (such as PCB) viasolder balls, or provide efficient electrical connection of asemiconductor chip to a substrate, a plurality of conductive traces suchas copper traces are formed on surfaces of the substrate and extended toform connecting pads where a nickel/gold metal layer is applied to allowconductive elements, such as gold wires, bumps or solder balls to beeffectively bonded to the connecting pads of the substrate andelectrically connect the substrate to the chip or PCB, and also toprevent the connecting pads from oxidization due to externalenvironmental influences. For forming the nickel/gold metal layer havinghigh electrical conductivity, during the fabrication of the substrate,the connecting pads are adapted to be electrically connected to aplating bus, such that a plating current can go through the plating busto the connecting pads and allow the nickel/gold metal layer to bedeposited on the connecting pads. When the semiconductor package isfabricated, the plating bus becomes useless and is removed.

A layout method of the TFBGA substrate is shown as FIG. 2. The TFBGAsubstrate 200 is divided into a plurality of substrate units 20 by aplurality of transverse cutting lines SLx and a plurality oflongitudinal cutting lines SLy. The substrate units 20 serve as packagesites to be subjected to subsequent packaging processes and would beseparated from each other by means of a final singulation processcutting along the cutting lines SLx and SLy. A circuit layout of eachsubstrate unit 20 includes a plurality of bonding pads 21, a pluralityof conductive through holes 22, and a plurality of conductive traces 23electrically connected to the bonding pads 21 and the conductive throughholes 22. The conductive through holes 22 are used to electricallyconnect the conductive traces 23 on a front surface of the substrateunit 20 to ball pads (not shown) on a back surface of the substrate unit20. In order to electroplate a nickel/gold metal layer on the bondingpads 21 on the front surface and the ball pads on the back surface ofthe substrate unit 20, the conductive through holes 22 are adapted to beelectrically connected to a plating bus 24 formed around each substrateunit 20, so that a plating current can go through the plating bus 24 toall the conductive through holes 22 and then to the bonding pads 21 andthe ball pads of the substrate unit 20. The plating bus 24 is formed ina grid shape and located on the cutting lines SLx and SLy, such that theplating bus 24 can be removed during the final singulation process.Related prior arts include U.S. Pat. Nos. 6,281,047, 6,319,750 and6,479,894.

However, the above layout method for the substrate has a plurality ofdrawbacks. Since the plating bus is formed around the substrate units,before the substrate units are singulated, electrical tests cannot beperformed on the substrate units. As a result, if inner-layer circuitsof the substrate units generally for signal connection and grounding orpowering purposes are incurred with defective appearance during thesubstrate fabrication, this situation would not be realized, and suchsubstrate units would still be subjected to subsequent die-bonding andpackaging processes if the substrate units have good outer-layercircuits and bonding pads or ball pads. This not only causes a waste ofmaterials and cost but also leads to an increase in fabrication stepsand time, as well as sacrifices the client's good dies due tofabrication of products with defective inner-layer circuits as it isincapable of detecting failure of the inner-layer circuits at an earlierstage.

Therefore, the problem to be solved here is to provide a method forindicating whether inner-layer circuits of a substrate are good and thusindicating whether the substrate should be subjected to subsequentpackaging processes, so as to prevent a waste of materials and cost, anincrease in fabrication steps and time, and sacrifice of the client'sgood dies from occurrence.

SUMMARY OF THE INVENTION

In light of the above drawbacks in the prior art, a primary objective ofthe present invention is to provide a circuit board with aquality-indicator mark and a method for indicating the quality of thecircuit board, so as to effectively inspect whether inner-layer circuitsof the circuit board are good during fabrication processes.

Another objective of the present invention is to provide a circuit boardwith a quality-indicator mark and a method for indicating the quality ofthe circuit board, which can avoid a waste of materials and an increasein fabrication cost for semiconductor packaging processes.

Still another objective of the present invention is to provide a circuitboard with a quality-indicator mark and a method for indicating thequality of the circuit board, which can avoid unnecessary performance ofsteps and unnecessary usage of time for semiconductor packagingprocesses.

A further objective of the present invention is to provide a circuitboard with a quality-indicator mark and a method for indicating thequality of the circuit board, so as to avoid the client's good diesbeing sacrificed.

In accordance with the above and other objectives, the present inventionproposes a circuit board with a quality indicator mark, comprising aplurality of circuit board units each having a multi-layer circuitstructure; at least one conductive mark formed on a surface of each ofthe circuit board units; and a plating bus formed around each of thecircuit board units, wherein the plating bus is electrically connectedto the circuit structure of each of the circuit board units and isselectively electrically connected to the conductive mark via a platingtrace formed in an inner-layer circuit structure of the circuit boardunit and via interconnections in the circuit board unit.

The present invention also proposes a method for indicating quality of acircuit board with a quality-indicator mark. The method comprises thesteps of: providing a circuit board having a plurality of circuit boardunits, wherein each of the circuit board units has an inner-layercircuit structure, and a plating bus is formed around each of thecircuit board units and extended to form a plating trace in theinner-layer circuit structure; inspecting whether the inner-layercircuit structure of each of the circuit board units is good; if yes,maintaining the connection between the plating trace and the plating busof the circuit board unit; if no, breaking the connection between theplating trace and the plating bus of the circuit board unit; and formingat least one circuit structure on the inner-layer circuit structure ofeach of the circuit board units, and forming a conductive structure onthe plating trace to provide a conductive mark on a surface of thecircuit board unit, as well as forming a metal protective layer via theplating bus on the at least one circuit structure of the circuit boardunit, such that the conductive mark formed with the metal protectivelayer indicates that the corresponding circuit board unit has theplating bus being connected to the plating trace and the inner-layercircuit structure thereof is good.

In the use of the circuit board with a quality-indicator mark and themethod for indicating quality of the circuit board in the presentinvention, if during the fabrication processes of the multi-layercircuit board, the inner-layer circuit structure of each circuit boardunit is inspected having good quality, the electrical connection betweenthe plating trace and the plating bus of the circuit board unit would bemaintained. Then, at least one circuit structure is formed on theinner-layer circuit structure, and a conductive structure is provided onthe plating trace and electrically connected to the conductive mark.During formation of the metal protective layer on the at least onecircuit structure of the circuit board unit via the plating bus, themetal protective layer can also be formed on the conductive mark via theplating bus and the plating trace. This thus indicates that theinner-layer circuit structure is good and the corresponding circuitboard unit can be subjected to subsequent die-bonding and packagingprocesses.

On the contrary, if during the fabrication processes of the multi-layercircuit board, the inner-layer circuit structure of the circuit boardunit is inspected not having good quality, the electrical connectionbetween the plating trace and plating bus of the circuit board unitwould be broken. Then, at least one circuit structure is formed on theinner-layer circuit structure, and a conductive structure is provided onthe plating trace and electrically connected to the conductive mark.During formation of the metal protective layer on the at least onecircuit structure of the circuit board unit via the plating bus, sincethe electrical connection between the plating trace and the plating busis broken, the metal protective layer would not be deposited on theconductive mark. This thus indicates that the inner-layer circuit is notgood and the corresponding circuit board unit should not subjected tosubsequent die-bonding and packaging processes so as not to cause awaste of materials and cost and an increase in fabrication steps andtime, thereby assuring the client's rights and interests.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be more fully understood by reading thefollowing detailed description of the preferred embodiments, withreference made to the accompanying drawings, wherein:

FIGS. 1A to 1D (PRIOR ART) are schematic cross-sectional diagramsshowing procedural steps of a conventional fabrication method for acircuit board;

FIG. 2 (PRIOR ART) is a schematic diagram showing a circuit layout of aconventional TFBGA substrate;

FIG. 3A is a schematic diagram of a circuit board with aquality-indicator mark according to the present invention;

FIG. 3B is a cross-sectional view of a circuit board unit according tothe present invention;

FIG. 4A is a cross-sectional view showing electrical disconnectionbetween a plating trace and a plating bus in the circuit board unitaccording to the present invention; and

FIG. 4B is a schematic diagram showing failure to form a metalprotective layer on a conductive mark during deposition of the metalprotective layer on the circuit board unit via the plating bus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 3A shows a circuit board with a quality-indicator mark according tothe present invention. The circuit board 300 is a circuit board platecomprising a plurality of circuit board units 30 divided by a pluralityof transverse and longitudinal cutting lines 31. A plating bus 32 isformed at the cutting lines 31 and encircles each of the circuit boardunits 30. The plating bus 32 is extended and electrically connected tocircuit structures of the circuit board units 30, such as bonding pads33, conductive vias 34, and conductive traces 35 that are extended andelectrically connected to the bonding pads 33 and the conductive vias34. The conductive vias 34 are used to electrically connect the bondingpads 33 on a front surface of the circuit board units 30 to ball pads(not shown) on a back surface of the circuit board units 30 viainterconnections between layers of the circuit board units 30.

FIG. 3B is a cross-sectional view of a circuit board unit according tothe present invention. The circuit board unit 30 has a multi-layerstructure, including a core 30 a and a build-up circuit layer 30 bformed on each of front and back surfaces of the core 30 a. The platingbus 32 is extended to form a plating trace 320 in an inner-layer circuitstructure 301 a of the circuit board unit 30 at the build-up circuitlayer 30 b on the front surface of the core 30 a. A conductive via 36 isformed at a terminal of the plating trace 320. At least one conductivemark 37 is formed on the conductive via 36 and located at the build-upcircuit layer 30 b on the front surface of the core 30 a. Subsequently,a solder mask layer 38 such as green paint can be applied on the frontand back surfaces of the circuit board unit 30 to protect circuitstructures on the surfaces of the circuit board unit 30. The solder masklayer 38 has a plurality of openings 380 for exposing the conductivemark 37 and input/output (I/O) connections (such as bonding pads 33 andball pads 330) of the circuit board unit 30, wherein the exposed I/Oconnections are used to electrically connect the circuit board unit 30to an external device (not shown). This allows a metal protective layer39 such as nickel/gold metal layer to be electroplated on the exposedI/O connections and conductive mark 37 via the plating bus 32. It shouldbe noted that beside the front surface of the circuit board unit 30where the bonding pads 33 are situated, the conductive mark 37 can alsobe formed on the back surface of the circuit board unit 30 where theball pads 330 are provided. Further, the conductive mark 37 can belocated not only outside an area encompassed by the plating buses 32(FIG. 3A) on the circuit board unit 30 but also within the areaencompassed by the plating bus 32 not having a circuit layout of thecircuit board unit 30. Moreover, the circuit board unit 30 is notlimited to a four-layer circuit structure but may have any number ofmultiple circuit layers. Also, any one or more of the inner circuitlayers of the multi-layer circuit board unit can be provided withplating traces electrically connected to the plating bus, allowingconductive marks to be formed on the surfaces of the circuit board unitand electrically connected to the plating traces via interconnectionsbetween layers of the circuit board unit.

Whether the plating trace 320 remains being electrically connected tothe plating bus 32 or not is used to indicate whether inner-layercircuits of the circuit board are good or not in quality after thecircuit board is fabricated and to determine whether subsequentdie-bonding and packaging processes are to be performed on the circuitboard. More specifically, during the fabrication of the circuit board,if the inner-layer circuit structure 301 a of the circuit board unit 30is visually inspected having good appearance, the electrical connectionbetween the plating trace 320 formed in the inner-layer circuitstructure 301 a and the plating bus 32 is maintained as shown in FIG.3B, allowing at least one build-up circuit layer 30 b to be formed onthe inner-layer circuit structure 301 a, and allowing the conductive via36 to be formed on the plating trace 320 and electrically connected tothe conductive mark 37 on the surface of the circuit board unit 30. Assuch, the metal protective layer 39 can be subsequently electroplated onthe bonding pads 33 or ball pads 330 of the circuit board unit 30 andalso on the conductive mark 37 via the plating bus 32, as shown in FIGS.3B and 4B. This thus indicates that the inner-layer circuit structure301 a of the circuit board unit 30 is good in quality, and the circuitboard unit 30 can be subjected to subsequent die-bonding and packagingprocesses.

Contrarily, if the inner-layer circuit structure 301 a of the circuitboard unit 30 is visually inspected not having good appearance duringfabrication of the circuit board 300, the plating trace 320 formed inthe inner-layer circuit structure 301 a is electrically disconnectedfrom the plating bus 32 to form an open circuit S, as shown in FIG. 4A.Subsequently, at least one build-up circuit layer 30 b is formed on theinner-layer circuit structure 301 a, and the conductive via 36 is formedon the plating trace 320 and electrically connected to a conductive mark37′ on the surface of the circuit board unit 30. During electroplatingof the metal protective layer 39 on the bonding pads 33 or ball pads 330via the plating bus 32, since the plating trace 320 and the plating bus32 form the open circuit S, the metal protective layer 39 cannot bedeposited on the conductive mark 37′, as shown in FIG. 4B. This thusindicates that the inner-layer circuit structure 301 a of the circuitboard unit 30 is defective in quality, and the circuit board unit 30should not undergo subsequent die-bonding and packaging processes so asnot to cause a waste of materials and cost and an increase infabrication steps and time, thereby avoiding the client's good diesbeing sacrificed.

The invention has been described using exemplary preferred embodiments.However, it is to be understood that the scope of the invention is notlimited to the disclosed embodiments. On the contrary, it is intended tocover various modifications and similar arrangements. For example, theinvention is not limited to the use with a TFBGA (thin flat ball gridarray) semiconductor package but can be applied to any circuit boardwith a multi-layer circuit structure to indicate whether the inner-layercircuit structure thereof is good in quality and determine whethersubsequently packaging processes are to be performed on the circuitboard. The scope of the claims, therefore, should be accorded thebroadest interpretation so as to encompass all such modifications andsimilar arrangements.

1-13. (canceled)
 14. A method for indicating quality of a circuit boardwith a quality-indicator mark, comprising the steps of: providing acircuit board having a plurality of circuit board units, wherein each ofthe circuit board units has an inner-layer circuit structure, and aplating bus is formed around each of the circuit board units andextended to form a plating trace in the inner-layer circuit structure;inspecting whether the inner-layer circuit structure of each of thecircuit board units is good; if yes, maintaining the connection betweenthe plating trace and the plating bus of the circuit board unit; if no,breaking the connection between the plating trace and the plating bus ofthe circuit board unit; and forming at least one circuit structure onthe inner-layer circuit structure of each of the circuit board units,and forming a conductive structure on the plating trace to provide aconductive mark on a surface of the circuit board unit, as well asforming a metal protective layer via the plating bus on the at least onecircuit structure of the circuit board unit, such that the conductivemark formed with the metal protective layer indicates that thecorresponding circuit board unit has the plating bus being connected tothe plating trace and the inner-layer circuit structure thereof is good.15. The method of claim 14, wherein a solder mask layer is formed onsurfaces of the circuit board and has a plurality of openings forexposing the conductive marks and input/output connections of thecircuit board units.
 16. The method of claim 15, wherein theinput/output connections include bonding pads and ball pads.
 17. Themethod of claim 14, wherein the metal protective layer is a nickel/goldmetal layer.
 18. The method of claim 14, wherein the circuit board unitsare divided by a plurality of transverse and longitudinal cutting lines,and the plating bus is formed at the transverse and longitudinal cuttinglines.
 19. The method of claim 14, wherein the plating trace is providedwith a conductive via at a terminal thereof, and the conductive mark isformed on the conductive via and located at the at least one circuitstructure of the circuit board unit.
 20. The method of claim 14, whereinthe conductive mark is selectively formed on a front surface or a backsurface of the circuit board unit.
 21. The method of claim 14, whereinthe conductive mark is selectively located outside an area encompassedby the plating bus on the circuit board unit or within the areaencompassed by the plating bus free of a circuit layout of the circuitboard unit.